Conventionally in a vehicle such as a van having box-shaped body, a space for occupants and a space for luggage are made of a common space. Therefore, a rear seat(s) is designed to change positions, i.e., from a seating position for enabling an occupant to be seated thereon to a walk-in position at which a seatback is forwardly tilted for enabling an occupant to enter a rear space of the vehicle, or to a tilt-down position where the seatback is forwardly tilted (folded) to be substantially horizontal when placing objects (such as luggage) on a back surface of the seatback. According to JP2004-243864A (hereinafter, referred to as reference 1), a seat apparatus includes a slide lock releasing means for releasing a locked state of a slide lock mechanism by a rotation of an operation lever located at a first position in a first direction and a reclining lock releasing means. The reclining lock releasing means releases a locked state of a reclining mechanism by the rotation of the operational lever located at a second position in the first direction. Thus, by operating one operation lever in different manner, a lock release of the seat slide mechanism, a lock release of the reclining mechanism and a retraction of the seat are performed.
Further, according to JPU1994-27297A (hereinafter, referred to as reference 2), a pin is locked by a hook of a locking member when forwardly tilting an upper arm of a seatback, and the upper arm is accordingly prevented from pivoting in a backward direction. Further, a lower end portion of a memory protrusion-detecting member is pressed upwardly by a memory protrusion when an upper rail of a seat apparatus slides. Therefore, a generated counterforce is received by a lower end portion of the locking member to pivot the locking member, thereby releasing the lock between the hook and the pin to allow the upper arm to pivot in the backward direction. Further, in cooperation with the backward pivoting movement of the upper rail, the upper rail is locked to a lower rail of the seat apparatus. Thus, even in a state where a vibration of the seat apparatus is severe, a slide lock mechanism is prevented from malfunctioning.
However, according to the references 1 and 2, a mechanism for performing both of an operation to move the seatback to the walk-in position and an operation to move the seatback to the tilt-down position is not disclosed. Further, when structuring a mechanism for performing both of the operations to move the seatback to the walk-in position and to the tilt-down position, an intermediate position lock portion is required to be provided between a seating position at which an occupant is able to be seated and the tilt-down position at which the seatback is reclined to be substantially horizontal, so that the seatback is locked to be retained at the walk-in position while pivotally moving towards the tilt-down position. However, in a condition where a manual operation for retaining the seatback is simultaneously performed when performing an operation of a lever for moving the seatback to the walk-in position, the intermediate position locking portion may fail to lock the seatback so that the seatback may be pivotally moved to the tilt-down position without being locked at the walk-in position. Thus, a malfunction of the seat apparatus may occur.
A need thus exists for a seat apparatus for a vehicle which is not susceptible to the drawback mentioned above.